1. Field of the Invention
The present invention relates to a carburetor in which a jet needle inserted into a needle jet controls the amount of fuel supply. An internal combustion engine mounted on a motorcycle is equipped with the type of carburetor.
2. Description of Background Art
A type of carburetor that has been known as one for internal combustion engine of motorcycle is equipped with a needle jet and a jet needle. In this type of carburetor, the needle jet is disposed as extending in the up and down directions, and the fuel is supplied to the air intake tube through the upper end portion of the needle jet. Meanwhile, the jet needle, which is inserted into the needle jet, is provided to the throttle valve. For details, refer to Japanese Patent Application Laid-Open Publication No. Hei 10-26053.
Some motorcycles, such as off-road motorcycles, run with occasional big jumps. In a carburetor of the engine mounted on a motorcycle of this kind, an inertial force acts on the fuel inside the needle jet (hereinbelow referred to as “fuel-in-jet”) at the time of landing after a jump, and the fuel-in-jet is accelerating downward. A large acceleration of this direction makes the fuel-in-jet move downward. The fuel-in-jet sometimes flows out of the needle jet, then passes through the main fuel jet, and then flows back to the float chamber. With such a reverse flow, the fuel-in-jet lessens, which temporarily reduces the fuel delivery from the needle jet to the air intake tube. The lean air-fuel mixture thus produced reduces the engine output.
The present invention has been made in view of the problem mentioned above. An object of the present invention is to prevent the carburetor equipped with a needle jet from producing a lean air-fuel mixture that may possibly be produced, though temporarily, when the fuel in the needle jet is accelerating downward.